My player is double jumping when it should not be able to. I am not sure what is allowing it to do so.

I wrote a script to allow my player to perform a "charged" jump. The longer the space bar is held down the more power is added to the minimum jump. The code is working exactly as it should be, but it's also allowing a double jump. The air jumping is not infinite. It's limited to only one jump, but I still need to remove it. How do I allow the player to jump only when touching the ground?

 var onGround :boolean = false;
 var jumpPressure : float = 0;
 var minJump : float = 5;
 var maxJumpPressure : float = 10;
 var rigid : Rigidbody;
 var maxAngle = 80;
 
 
 function Start () {
 
     rigid = GetComponent.<Rigidbody>();
 }
 
 function Update () {
   
     // If the player is on the ground
     if(onGround == true) {
        
         // If the player presses jump
         if(Input.GetKey("space")){
            
             // Begin building Pressure
             if (jumpPressure < maxJumpPressure){
            
                 jumpPressure += Time.deltaTime * 10;
             }
            
             // Once the pressure is at the max, keep it there
             else {
                
                 jumpPressure = maxJumpPressure;
             }
         }
        
             // If the player isn't pressing jump
         else {
           
             if (jumpPressure > 0) { 
 
                 jumpPressure = jumpPressure + minJump;
                 rigid.velocity = new Vector3 (0, jumpPressure, 0);
                 jumpPressure = 0;
                 onGround = false;
 
             }
 
         }
     }
 }
 
 // Check if the player is on the ground
 function OnCollisionStay (collision : Collision) {
 
     for (var contact : ContactPoint in collision.contacts) {
 
         if (Vector3.Angle(contact.normal, Vector3.up) < maxAngle) {
 
             onGround = true;
         }
     }
 
 }